[RUM-16486] Add .viewUpdates flag with delta projection in RUMViewScope

[maxep]

What and why?

Integrates RUMViewUpdateEvent delta projection into RUMViewScope, gated behind a new .viewUpdates Feature Flag.

When the flag is enabled, the first write per view emits a full RUMViewEvent, every subsequent write emits a RUMViewUpdateEvent containing only the fields that changed relative to the previous full event.

How?

• Inject .viewUpdates feature flag through RUM.Configuration.FeatureFlag, RUMScopeDependencies, and RUMFeature.
• RUMViewScope tracks lastSentViewEvent and writes a delta (RUMViewEvent.update(from:)) instead of the full event when the flag is enabled.
• RUMViewScope_Tests mirrors the existing view scope test suite with the flag enabled, asserting dual-event-type routing.

Review checklist

• Feature or bugfix MUST have appropriate tests (unit, integration)
• Make sure each commit and the PR mention the Issue number or JIRA reference
• Add CHANGELOG entry for user facing changes
• Add Objective-C interface for public APIs - see our guidelines (internal)
• Run make api-surface when adding new APIs

[datadog-datadog-prod-us1]

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⚠️ Warnings

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DataDog/dd-sdk-ios | Unit Tests (iOS)     

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